The present invention relates to a seatbelt retractor that winds and unwinds the webbing of the seat belt. More specifically, the present invention relates to a seatbelt retractor that includes an energy absorbing mechanism (EA mechanism) that restrains a load applied to the webbing by a torsion bar when the unwinding of the seatbelt is prevented in case of emergency such as a crash in which a large extent of deceleration of the vehicle is affected with the webbing fastened.
Hitherto, the seatbelt apparatus mounted on the vehicle such as automotive vehicles prevents jumping out of the passenger from the seat and thus protects the passenger by restraining the passenger with webbing in case of emergency described above.
Such a seatbelt apparatus is provided with a seatbelt retractor for winding the webbing. In the seatbelt retractor, the webbing is wound on the reel when it is not used, but pulled out and fastened on the passenger when it is used. In the seatbelt retractor, the locking mechanism is actuated in case of emergency as described above to prevent rotation of the reel in the unwinding direction, and thus unwinding of the webbing is prevented. Therefore, the passenger is positively restrained and protected in case of emergency.
Incidentally, in the seatbelt retractor of the conventional seatbelt apparatus, when the webbing restrains and protects the passenger in case of emergency such as a crash of the vehicle, a large extent of deceleration of the vehicle occurs and thus the passenger is apt to move forward by large inertia. Therefore, the webbing is applied with a large load and the passenger is applied with a large impact from the webbing. Though the large impact is a minor matter for the passenger, it is preferable to be restrained if it is possible.
Therefore, various seatbelt retractors comprising an EA mechanism for restraining a load applied to the webbing by a torsion bar in case of emergency with the webbing fastened has been conventionally proposed.
In the seatbelt retractor comprising an EA mechanism, the reel for winding the webbing and the locking base of the locking mechanism for locking the rotation of the reel in the webbing unwinding direction in case of emergency are rotatably (so as to be capable of transmitting a torque) connected by a torsion bar. When the locking mechanism is actuated in case of emergency, rotation of the locking base in the webbing unwinding direction is prevented, but the torsion bar is twisted because unwinding of the webbing due to inertia of the passenger makes the reel rotate in the webbing unwinding direction. Subsequently, the reel rotates in the webbing unwinding direction while twisting the torsion bar, and a load applied to the webbing by a torsional torque of the torsion bar is restricted and thus the impact applied to the passenger is absorbed and alleviated.
When the torsion bar is rotatably connected to the reel and the locking base, axial holes of hexagonal cross section are respectively formed at the center positions of the reel and the locking base, and torque transmitting shafts of hexagonal cross section are respectively provided on the torsion bar at the position where the reel and the locking base are rotationally connected, so that the torque transmitting shafts are press-fined into the axial holes on the reel and the locking base. In this case, in order to prevent backlash at the time of press-fitting, three backlash preventing ribs i, j, k are conventionally provided respectively at the centers of the three sides c, e, g, which are not adjacent, out of six arc-shaped sides c, d, e, f g, and h of the axial hole b having a hexagonal cross section formed on the reel a as shown in FIG. 7, for example, to fix and support the torsion bar m. Likewise, three backlash preventing ribs are also formed on the center positions of three arc-shaped sides of the axial hole having hexagonal cross section formed on the locking base, though it is not shown.
However, providing backlash preventing ribs i, j, k at the center positions of the sides c, e, g of the hexagonal cross section of the axial hole b as in the conventional case has a following problem. That is, when a load is applied to the webbing at the time when the lock of the locking mechanism is actuated and the webbing is being unwound, the reel a is apt to rotate in the webbing unwinding direction CW as shown in FIG. 7, and a large force to rotate the torsion bar m is applied from the reel a to the torsion bar m. At this time, since the large force is applied to the torsion bar m via the backlash preventing ribs i, j, k at the center positions of sides c, e, g of the axial hole b, the backlash preventing ribs i, j, k are collapsed and thus a gap is generated between the reel and the torsion bar. Such a gap between the axial hole in the reel b and the torsion bar m causes backlash and thus contributes to generate squeak and rattle. Likewise, a gap is also generated between the torsion bar m and the locking base.
Therefore, it is an object of the present invention to provide a seatbelt retractor that can positively prevent backlash between the torsion bar and the member in which the torsion bar is fitted even when a large force is applied to the torsion bar when the lock of the locking mechanism is actuated.